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Elephant walking

Bison galloping

This is an article on gaits of all animals; for other meanings, see: Gait (disambiguation).

Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency. Different animal species may use different gaits due to differences in anatomy that prevent use of certain gaits, or simply due to evolved innate preferences as a result of habitat differences. While various gaits are given specific names, the complexity of biological systems and interacting with the environment make these distinctions 'fuzzy' at best. Gaits are typically classified according to footfall patterns, but recent studies often prefer definitions based on mechanics. The term typically does not refer to limb-based propulsion through fluid mediums such as water or air, but rather to propulsion across a solid substrate by generating reactive forces against it (which can apply to walking while underwater as well as on land).

Due to the rapidity of animal movement, simple direct observation is rarely sufficient to give any insight into the pattern of limb movement. In spite of early attempts to classify gaits based on footprints or the sound of footfalls, it wasn't until Eadweard Muybridge and Étienne-Jules Marey began taking rapid series of photographs that proper scientific examination of gaits could begin.

Look up gait in Wiktionary, the free dictionary.

Overview[link]

Milton Hildebrand pioneered the scientific analysis and the classification of gaits. The movement of each limb was partitioned into a stance phase, where the foot was in contact with the ground, and a swing phase, where the foot was lifted and moved forwards. Each limb must complete a cycle in the same length of time, otherwise one limb's relationship to the others can change with time, and a steady pattern cannot occur. Thus, any gait can completely be described in terms of the beginning and end of stance phase of three limbs relative to a cycle of a reference limb, usually the left hindlimb.

Variables[link]

Gait graphs in the style of Hildebrand. Dark areas indicate times of contact, bottom axis is % of cycle

Gaits are generally classed as "symmetrical" and "asymmetrical" based on limb movement. It is important to note that these terms have nothing to do with left-right symmetry. In a symmetrical gait, the left and right limbs of a pair alternate, while in an asymmetrical gait, the limbs move together. Asymmetrical gaits are sometimes termed "leaping gaits", due to the presence of a suspended phase.

The key variables for gait are the duty factor and the forelimb-hindlimb phase relationship. Duty factor is simply the percent of the total cycle which a given foot is on the ground. This value will usually be the same for forelimbs and hindlimbs unless the animal is moving with a specially-trained gait or is accelerating or decelerating. Duty factors over 50% are considered a "walk", while those less than 50% are considered a run. Forelimb-hindlimb phase is the temporal relationship between the limb pairs. If the same-side forelimbs and hindlimbs initiate stance phase at the same time, the phase is 0 (or 100%). If the same-side forelimb contacts the ground half of the cycle later than the hindlimb, the phase is 50%.

Differences between species[link]

Any given animal uses a relatively restricted set of gaits, and different species use different gaits. Almost all animals are capable of symmetrical gaits, while asymmetrical gaits are largely confined to mammals, who are capable of enough spinal flexion to increase stride length (though small crocodilians are capable of using a bounding gait). Lateral sequence gaits during walking and running are most common in mammals, but arboreal mammals such as monkeys, some possums, and kinkajous use diagonal sequence walks for enhanced stability. Diagonal sequence walks and runs (aka trots) are most frequently used by sprawling tetrapods such as salamanders and lizards, due to the lateral oscillations of their bodies during movement. Bipeds are a unique case, and most bipeds will display only three gaits - walking, running, and hopping - during natural locomotion. Other gaits, such as human skipping, are not used without deliberate effort.

Physiological effects of gait[link]

Gait choice can have effects beyond immediate changes in limb movement and speed, notably in terms of ventilation. Because they lack a diaphragm, lizards and salamanders must expand and contract their body wall in order to force air in and out of their lungs, but these are the same muscles used to laterally undulate the body during locomotion. Thus, they cannot move and breathe at the same time, a situation called Carrier's constraint, though some, such as monitor lizards, can circumvent this restriction via buccal pumping. In contrast, the spinal flexion of a galloping mammal causes the abdominal viscera to act as a piston, inflating and deflating the lungs as the animal's spine flexes and extends, increasing ventilation and allowing greater oxygen exchange.

Energy-based gait classification[link]

While gaits can be classified by footfall, new work involving whole-body kinematics and force-plate records has given rise to an alternative classification scheme, based on the mechanics of the movement. In this scheme, movements are divided into walking and running. Walking gaits are all characterized by a 'vaulting' movement of the body over the legs, frequently described as in inverted pendulum (displaying fluctuations in kinetic and potential energy which are perfectly out of phase). In running, the kinetic and potential energy fluctuate in-phase, and the energy change is passed on to muscles, bones, tendons and ligaments acting as springs (thus it is described by the spring-mass model).

Energetics[link]

Speed generally governs gait selection, with quadrupedal mammals moving from a walk to a run to a gallop as speed increases. Each of these gaits has an optimum speed, at which the minimum calories per meter are consumed, and costs increase at slower or faster speeds. Gait transitions occur near the speed where the cost of a fast walk becomes higher than the cost of a slow run. Unrestrained animals will typically move at the optimum speed for their gait to minimize energy cost.

Non-tetrapod gaits[link]

In spite of the differences in leg number shown in terrestrial vertebrates, according to the inverted pendulum model of walking and spring-mass model of running, "walks" and "runs" are seen in animals with 2, 4, 6, or more legs. The term 'gait' has even been applied to flying and swimming organisms who produce distinct patterns of wake vortices.

See also[link]

• Gait analysis
• Gait (human)
• Gait (dog)
• Horse gait
• Parkinsonian Gait

References[link]

This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations. (August 2009)

• Hildebrand, M. (1989). "Vertebrate locomotion an introduction how does an animal's body move itself along?". BioScience 39 (39): 764–765. JSTOR 1311182. 
• Hoyt, D. F.; Taylor, R. C. (1981). "Gait and the energetics of locomotion in horses". Nature 292 (292): 239–240. DOI:10.1038/292239a0. http://www.nature.com/nature/journal/v292/n5820/abs/292239a0.html. 
• Carrier, D. (1987). "Lung ventilation during walking and running in four species of lizards". Experimental Biology 47 (1): 33–42. PMID 3666097. 
• Bramble, D. M.; Carrier, D. R (1983). "Running and breathing in mammals". Science 219 (4582): 251–256. DOI:10.1126/science.6849136. PMID 6849136. http://www.sciencemag.org/cgi/content/abstract/sci;219/4582/251. 
• Blickhan, R.; Full, R. J. (1993). "Similarity in multilegged locomotion: Bouncing like a monopode". Journal of Comparative Physiology A (173): 509–517. http://www.springerlink.com/content/k4n326302181t784/. 
• Cavagna, G. A.; Heglund, N. C.; Taylor, R. C. (1977). "Mechanical work in terrestrial locomotion: two basic mechanisms for minimizing energy expenditure". Am. J. Physiol 233 (5): R243–R261. PMID 411381. http://ajpregu.physiology.org/cgi/content/abstract/233/5/R243. 

Nico Muhly /ˈniːkoʊ ˈmjuːli/ (born August 26, 1981, in Vermont) is a contemporary classical music composer,^[1] who has worked and recorded with classical and pop/rock musicians. He currently lives in the Lower East Side section of Manhattan in New York City.

Biography[link]

Early years[link]

Muhly was born in Vermont and raised in Providence, Rhode Island. His mother, Bunny Harvey, is a painter and teacher at Wellesley College, and his father, Frank Muhly, is a documentary filmmaker.^[2]

As a child, Muhly sang in the choir at Grace Episcopal Church in Providence,^[3] and he started to study piano at 10.^[2]

Muhly went on to study at The Wheeler School in Providence, then moved on to Columbia University where he got his undergraduate degree in English and to the Juilliard School where he graduated with his Master's degree in Music and studied composition with John Corigliano and Christopher Rouse.

Musical works[link]

In 2005, Muhly was commissioned by Colorado Academy, a private school in Colorado, to write a song for the opening of their new Fine Arts building.

Muhly worked in collaboration with Björk on the DVD single "Oceania" in 2004,^[4] and he worked with Philip Glass as an editor, conductor, and keyboardist.^[4]

In 2006, he released his first album of works, titled Speaks Volumes. In 2008, he released his second album, titled Mothertongue.

In 2009, Muhly worked on various classical compositions with the Brooklyn-based indie-folk rock band Grizzly Bear on their third album, Veckatimest,^[5] and he worked with Antony and the Johnsons on the albums The Crying Light and Swanlights.

Muhly recently worked on two commissions for UK-based Britten Sinfonia, performed in January and February 2010.

The Gilmore International Keyboard Festival commissioned "Drones & Piano" for pianist Bruce Brubaker. The piece premiered in May 2010.^[6]

Muhly's opera Two Boys, a collaboration with librettist Craig Lucas and directed by Bartlett Sher, premiered in June 2011 at the English National Opera and will make its Metropolitan Opera debut during the 2013/2014 season.^[7][8][9] According to a New York Times article, the opera is based on a late-1990s British case involving a 14-year-old boy taking on the online identity of women to try to get someone to kill him, without success.^[10] However, in an interview with The Advocate, Muhly stated that the opera is based on the story of an online friendship between two male teenagers, one of whom kills the other.^[2]

The Saint Paul Chamber Orchestra, the Minnesota Commissioning Club, Cantus, the Andrew W. Mellon Foundation, and Alfred P. and Ann M. Moore commissioned "Luminous Body", also a collaboration with librettist Craig Lucas. The piece premiered on September 9, 2011.^[11]

Upcoming projects[link]

Six of Muhly's choral works are featured on a CD recorded by the Los Angeles Master Chorale, A Good Understanding, released by the Decca classics label.^[12]

Projects[link]

Arrangements and orchestrations[link]

• 2006 Letting Go by Bonnie 'Prince' Billy
• 2007 Miserere Mei (orchestration of William Byrd's Miserere Mei)
• 2007 Deus and Bow Thine Ear (orchestration of William Byrd's Deus and Bow Thine Ear)
• 2008 All Is Well by Sam Amidon
• 2008 "Með þér" and "Á meðan vatnið velgist" on Bestu kveðjur by Sprengjuhöllin
• 2009 Confessions, a multimedia collaboration with Teitur Lassen.^[15]
• 2009 Various songs on Antony and the Johnsons' album The Crying Light^[16]
• 2009 Various songs on Grizzly Bear's album Veckatimest
• 2009 Tricks of the Trade on Mew's album No More Stories...
• 2009 Year of the Dragon on Run Rabbit Run^[17]
• 2010 Various songs on Antony and the Johnsons' album Swanlights
• 2010 Go by Jónsi
• 2010 I See the Sign by Sam Amidon

Recordings[link]

• 2007 – Speaks Volumes (Bedroom Community HVALUR1CD) (Includes Clear Music; It Goes without Saying; Honest Music; Quiet Music; Pillaging Music; A Hudson Cycle and Keep in Touch)
• 2008 – Joshua (Original Motion Picture Soundtrack) by various artists (Moviescore Media)
• 2008 – Mothertongue (Bedroom Community HVALUR5CD) (Includes Mothertongue I: Archive; Mothertongue II: Shower; Mothertongue III: Hress; Mothertongue IV: Monster; Wonders: I. New Things & New Tidings; Wonders: II. The Devil Appear’d in the Shape of a Man; Wonders: III. A Complaint against Thomas Weelkes; The Only Tune: I. The Two Sisters; The Only Tune: II. The Old Mill Pond; and The Only Tune: III. The Only Tune)
• 2009 – The Reader (Original Motion Picture Soundtrack) by various artists (Lakeshore Records)
• 2009 – So Far Around the Bend by the National
• 2010 – I Drink the Air Before Me (Bedroom Community HVALUR10, Decca/Universal Classics 478 257)
• 2010 – A Good Understanding by Los Angeles Master Chorale (Includes many choral works) (Decca/Universal Classics 478 250)
• 2011 – Seeing is Believing by the Aurora Orchestra (Decca/Universal Classics 478 273. Released 10th June 2011.

References[link]

External links[link]

• Tim Page, "High Scorer," Smithsonian Magazine, October 2007. Retrieved on 2 March 2008.
• Andy Beta, "Of Transgendered Violas and Transatlanic Collaborators," City Pages, Issue: September 26, 2007, retrieved on 2 March 2008.
• Rebecca Mead, "Eerily Composed: Nico Muhly’s sonic magic," The New Yorker, February 11, 2008, retrieved on 2 March 2008.
• Molly Sheridan, "Composer on Fire: Defining Nico Muhly" (includes video), NewMusicBox, March 1, 2007, retrieved on 2 March 2008.
• Nico Muhly, 'Walls come tumbling down," The Guardian, October 5, 2007. Retrieved from Guardian.co.uk on 2 March 2008.
• List of published scores, Chester Music and Novello & Company, retrieved on 2 March 2008.
• Michaels, Sean (October 2008), "Nico Muhly [interview]", The Believer 6 (8): 72–77. 
• Official Web Site
• Myspace Page
• Nico Muhly on Brassland Records
• Nico Muhly at Now magazine
• Nico Muhly Bio